Migration distance as a selective episode for wing morphology in a migratory insect

D. T. Tyler Flockhart,Blair Fitz-gerald,Lincoln P. Brower,Leonard I. Wassenaar,D. Ryan Norris,Keith A. Hobson,Rachael Derbyshire,Sonia Altizer

doi:10.1186/s40462-017-0098-9

Abstract

BackgroundSelective pressures that occur during long-distance migration can influence morphological traits across a range of taxa. In flying insects, selection should favour individuals that have wing morphologies that increase energy efficiency and survival. In monarch butterflies, differences in wing morphology between migratory and resident populations suggest that migratory populations have undergone selection for larger (as measured by length and area) and more elongated (as measured by roundness and aspect ratio) forewings. However, selection on wing morphology may also occur within migratory populations, particularly if individuals or populations consistently migrate different distances.ResultsUsing 613 monarch butterflies that were collected on the Mexican wintering grounds between 1976 – 2014, we tested whether monarch wing traits were associated with migratory distance from their natal areas in eastern North America (migration range: 774–4430 km), as inferred by stable-hydrogen (δ2H) and -carbon (δ13C) isotopic measurements. Monarchs that migrated farther distances to reach their overwintering sites tended to have longer and larger wings, suggesting positive selective pressure during migration on wing length and area. There was no relationship between migration distances and either roundness or aspect ratio.ConclusionsOur results provide correlative evidence that the migratory period may act as a selective episode on monarch butterfly wing morphology, although selection during other portions of the annual cycle, as well as extensive mixing of individuals from various natal locations on the breeding grounds, likely counteracts directional selection of migration on morphology.

Highlights

Selective pressures that occur during long-distance migration can influence morphological traits across a range of taxa
Migratory distance was correlated with δ2H values but this relationship was not linear (Additional file 1: Figure S1), suggesting that our twoisotope assignment approach was likely a better estimate of migration distance than using δ2H values alone
The parameter estimates were in the predicted direction, monarchs that migrated longer distances did not have more pointed wings or larger aspect ratios (Table 1)

Summary

Introduction

Selective pressures that occur during long-distance migration can influence morphological traits across a range of taxa. Selection on wing morphology may occur within migratory populations, if individuals or populations consistently migrate different distances. The selective pressures associated with long-distance migration can influence morphology in a variety of taxa, including birds, insects and fish [1,2,3,4]. One way to estimate migratory distance of insects is through the use of endogenous markers such as stable isotopes [15, 16]. Stable isotope measurements have been used successfully to determine natal origin of migratory insects such as butterflies [22,23,24] and dragonflies [21]

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Discussion

Conclusion